Composite structure for forming a seal with glass



Sept. 20, 1949. A. HARRIS :rm. 2,432,178

COMPOSITE s'rnuc'nms FOR FORMING A SEAL WITH GLASS Filed Feb. 2 9 1944VE/V Toes E. A f/fl/PE/S I C. C. Farm/v 8) z. AM,

77'OENEY Patented Sept. 20, 1949 UNITED STATES PATENT OFFICE COMPOSITESTRUCTURE FOR FORMING A SEAL WITH GLASS Application February 29, 1944,Serial No. 524,504

3 Claims. 1

This invention relates to the art of sealing metal to glass andparticularly to a composite structure for forming a seal with glass.

The invention is particularly applicable to the sealing or uniting ofcopper and glass members used in some types of vacuum tubes in which theuniting of these members is a matter of material importance in order toprovide for electronic efliciency and reliability of such tubes. In thepractice of sealing copper to glass, the efliciency of the seal dependsupon the adherence of copper oxide to the base metal. A type ofoxygenfree high conductivity copper has been generally used for the tubemember and no difliculty was experienced due to a lack of oxideadherence, but diiiiculties are encountered in readily machining suchcopper members. By adding small amounts of tellurium or other suitableingredients, the machinability of the resultant copper alloy is greatlyimproved, but at the same time, due to the presence of the tellurium,the oxide scale flakes oif, thus preventing an effective seal.

Objects of the present invention are to provide a simple and practicableseal between a readily machinable metal alloy and glass, whereby theabove-referred-to difficulties encountered in forming an effective sealbetween such an alloy and lass are overcome.

In accordance with the above object, in one embodiment of the invention,a tellurium copper alloy member to be sealed to a glass member iselectroplated, or otherwise coated, upon a surface thereof to be unitedto the glass member, with pure copper of a suitable thickness, whichprovides an eifective barrier to prevent the migration of the telluriumto an oxidized surface of the copper coating on the copper alloy memberwhich unites it to the glass member, and thus the effectiveness of theseal is maintained.

Other objects and advantages of the invention will more fully appearfrom the following detailed description taken in conjunction with theaccompanying drawing, in which the single figure is a fragmentarylongitudinal section through a seal embodying the features of thisinvention as applied to the uniting of a glass tube and a copper alloymemberof a certain type of vacuum tube.

Referring to the drawing, wherein there is fragmentarily illustrated amachined tellurium copper alloy member i having a hollow frusto-conicalportion H, into which an open end of a glass tube I2 is entered andsealed, the effectiveness of the seal depending on the adherence ofcopper oxide formed on the surface of the tellurium copper al-. loymember to be united to the glass tube, the

member and tube forming a part of one type of vacuum tube. The member I0is mainly composed of oxygen-free high conductivity copper, to which hasbeen added a small amount, for ex- 5 ample, 25% to 2% of tellurium orsome other suitable ingredient, such as selenium or lead, to render theblank from which the member is formed more readily machlnable. Suchcopper, without the addition of a suitable ingredient. makes itdifiicult to machine a blank to the desired shape, On the other hand,the addition of tellurium, for example, to the copper has a deleteriousaction in that the tellurium tends to migrate to the surface of thecopper alloy member ID and, if a surface l3 thereof, which is to beunited or sealed to the glass tube i2, is not treated in a manner to bepresently described, it results in a poor seal between the parts, sincethe resultant oxidized surface upon which an effective seal dependstends to disintegrate and flake oil. To

overcome this dificulty, the surface l3 of the member Hi to be united tothe glass tube, I2 is first coated, by electroplating, or other suitablemeans, with pure copper of a suitable thickness. This coating of purecopper, indicated at H, is effective to prevent the. deleterious actionof the tellurium on the oxidized surface and thus the effectiveness ofthe seal is maintained.

In practicing a sealing method using the composite structure of thisinvention as applied to the sealing or uniting of the above-describedvacuum tube member In and glass tube ii, a tellurium copper alloy blankis first machined to the desired shape and then given the electroplatedpure copper coating l4 upon its inner surface i3, which is to be unitedto the glass tube. In some cases, it may be found desirable to machineor otherwise finish the inner surface of the pure copper coating H toprovide the desired fit be- 4O tween it and the surface of the glasstube l2.

After the above-described preparation, the member i0 and tube l2 may besupported in axial alignment in rotatable chucks and heated by asuitable gas torch, the copper alloy member ID 5 being heated at its endto be entered into the glass tube I! to red heat and the correspondingend of the tube heated until it is plastic and in this condition istapered to fit the inner conical face of the member iii. Such heating ofthe copper alloy member is continued until a good oxide coating isformed thereon. Following this, the tapered end of the rotating plasticglass tube i2 is longitudinally moved toward the rotating member i0 andgently set into it and held under a suitable pressure and, while so heldand with U the member and tube rotating, and while sub- Jected to heatof, for example, 1400' F. to 1600 F. from a gas torch for a suitableperiod, the sealing of the copper alloy member and glass tube iscompleted.

What is claimed is:

1. A composite structure for forming a seal with glass comprising amember composed of copper and teilurium for rendering the copper morereadily machinable, and a barrier coating thereon of substantially purecopper having an oxidized surface.

2. A composite structure for forming a seal with glass comprising amember composed of copper and an ingredient for rendering the same more15 Number rendering the same more readily machinable, 25

3 surface thereof, thus providing an excellent surface for the fusing ofglass thereto.

ROBERT A. HARRIS. CHARLES C. PATTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date 1,350,907 Yanai Aug. 24, 1920 1,649,907Mayer Nov. 22, 1927 1,692,998 Ruben Nov. 27, 1928 1,980,840 Wright eta1. Nov. 13, 1934 2,010,145 Eitel Aug. 6, 1935 2,038,136 Smith Apr. 21,1936 2,167,431 Bowie July 25, 1939 2,267,090 Freeman Dec. 23, 19412,268,939 Hensel Jan. 6, 1942

